Process for measuring and equalizing the gain characteristics of channel image intensifier arrays



April 21, 1970 K. J. HECKER 3,508,050 PROCESS FOR MEASURING AND EQUALIZING THE GAIN CHARACTERISTICS OF CHANNEL IMAGE INTENSIFIER ARRAYS Original Filed May 24, 1965 INPUT OUTPUT CHANNEL IMAGE INTENSIFIER ARRAY OUTPUT SINGLE FIBER ACCELERATING VOLTAGE FIG I VACUUM CHAMBER r 26 POWER 27 MEASURING SUPPLY AND 26 EQUIPMENT DEFLECTION AND POWER GENERATOR (ESLECTRW SUPPLY UN AND 24 DEFLECTOR sk fg 22 P POWER A VACUUM SUPPLY j p Mp IATMOSPHERE' EQUIPMENT J KLAUS J. HECKER INVENTOR.

ATTORNEYS United States Patent US. Cl. 25049.5 3 Claims ABSTRACT OF THE DISCLOSURE A process is disclosed for measuring and equalizing the gain characteristics of individual elements of a channel image intensifierarray. The channel image intensifier array consists of a plurality of tube elements stacked in parallel relationship having their inner surfaces of a conductive secondary emissive material and electrode means on each end thereof. An electron beam of variable intensity is directed at the input surface of the channel image intensifier array such that electrons emerge from the output surface of the array onto a collector plate. A measuring means is connected to the collector plate for measuring one-by-one the gain of the different elements of the array which in turn supplies this information to an electron beam deflection system which controls the electron beam such that the gain characteristics of the individual elements are equalized.

This is a division of application Ser. No. 45 8,523, filed May 24, 1965.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to improvements in channel image intensifier arrays making mass production of such arrays, with extremely uniform gain across their diameter, feasible.

It is an object of the invention to provide a system for producing uniform gain channel image intensifier arrays for use in image tubes for intensification of electron images.

Another object of the invention is to provide a novel process for measuring and equalizing the gain of individual elements of channel image intensifier arrays.

A further object of the invention is to provide a fast method of mass producing uniform channel image intensifier arrays.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic sketch showing a single hollow intensifier fiber and an array of such fibers.

FIG. 2 is a diagrammatic systems sketch showing one embodiment of a device for processing image intensifier arrays to produce an array of uniform gain intensifier fibers.

Referring now to the drawings like numerals refer to like parts in each of the figures.

Channel image intensifiers are used in image tubes for the intensification of electron images. The principle of a channel image intensifier is shown in FIG. 1. It consists of an array of many hollow fibers 12, usually made out of glass. The material itself, or a coating on the inside Cit 14 of the hollow fibers, is conductive and, in addition, has secondary electron emission properties. If a voltage is applied between electrodes mounted on either end of an array, a current will fiow through each fiber, resulting in a potential drop in each of the fibers. Electrodes are normally evaporated onto the surfaces of the input and output ends 15 and 16 of the individual hollow fibers 12 making up an array 10. Electrons entering the front or input end 15 of each individual fiber 12 will be accelerated by this electric field towards the output end 16 of the array. The electrons will, however, also hit and reflect along the walls of the fiber, causing emission of secondary electrons, which in turn are also accelerated, reflected, etc. Gains of up to 10 have been achieved in such fibers.

If an electron image is focused on the input surface of such an array 10, each fiber 12 will receive a number of electrons, depending upon the intensity of the electron image at the particular spot. At the output of the array, an intensified electron image will appear. However, if the gain of the different fibers of the array is not the same, the intensified image will not be a true reproduction of the original image. Since the gain of each fiber depends upon several different factors, it is extremely difficult to manufacture arrays of uniform gain. The present invention permits equalizing the gain of channel arrays produced thereby. To achieve this, a processing device is employed, one possible form of which is shown in FIG. 2. It consists of a high-vacuum chamber 20 (a demountable bell jar or the like) connected to the necessary vacuum pumps 20, etc.; a mounting fixture 24 inside the ball jar which permits the mounting and the operating of a channel image intensifier array 10, an electron gun 26 with a deflection system 20 capable of producing and directing an electron beam of variable intensity at any point of the input surface 15 of the channel array, and a collector plate 27 behind the channel array collecting all electrons emerging from the output surface 16 of the channel array. Collector plate 27 is connected to measuring equipment and a power supply 29 external to the bell jar. Additional equipment 30 may be required to obtain the necessary gas atmosphere inside the chamber 20, as hereinafter explained.

The processing device can be operated in two different modes: first, a measuring mode and, second, an equalizing mode. In the measuring mode the electron gun 26 produces an extremely low-current electron beam which is directed towards the array. The single particular fiber 12 of the array which is hit by the electron beam will multiply the number of electrons by the process described above and the resulting output signal from this fiber will be collected at the collector plate 27. Therefore, by this means, it is possible to measure the gain of each of the different fibers of the array.

In the equalizing mode, the electron gun 26 produces a high current electron beam, which similarly is directed towards the array. The high energy contained in this beam is used to etfect changes in gain. One process uses this energy to cause evaporation of part of the secondary emission coating 14 in a fiber '12 that is hit by the electron beam, resulting in a lower gain. In a diiferent arrangement, the chamber 20 contains a low-pressure atmosphere of, for example, oxygen supplied by gas equipment 30. In this arrangement, the fibers of the array to be equalized are coated with a material which, after oxydization, will be .a secondary electron emitting material (i.e., magnesium oxyd), but in contrast to the normal manufacturing process the material is only partially oxydized. If one fiber 12 of this array is now hit by the high energy electron beam, it will be heated and oxydization will take place, resulting in a higher gain in that particular fiber.

The gain of the fiber can be measured after one of the above processes has been used to change the gain of the fiber. If the gain still does not equal the desired gain, th process can be repeated until the desired gain results. After the gain equals the desired gain, electron gun 26 is pointed towards the next fiber 12 and the process is repeated. Obbiously, the whole operation can be controlled by automatic equipment in 28 and 29.

The process of the present invention makes econornically feasible the mass production of channel image intensifier arrays since it eliminates the need for extremely accurate conditions during the manufacture of the arrays, and it reduces the percentage of rejects drastically. Alternately, the electron beam is scanned constantly over the array, and the modes of operation are quickly alternated. When the beam hits the next fiber, it is adjusted first to measure the gain, and then quickly switched to the equalizing mode at an intensity determined by the difference between the desired gain and the measured gain. Then the beam is deflected to the next fiber. After one complete scan, the process is repeated until the gains of all fibers are the same.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A process for measuring and equalizing the gain characteristics of the individual elements of a channel image intensifier array, of the type consisting of a plurality of tube elements stacked in parallel relationship having their inner surface of conductive secondary emissive material and having electrode means on either end thereof, comprising:

(a) in a controlled atmosphere, alternately measuring and changing the gain of each individual element of a channel image intensifier array,

(b) measuring the gain of each element with a lowcurrent electron beam,

(0') changing the gain of each array element by subjecting the conductive secondary electron emissive inner surface of each said array element with a highcurrent electron beam to effect the gain thereof,

((1) repeating said measuring and changing of the gain of an element until the gain equals the desired gain,

(c) after the gain of an element equals the desired gain, repeating the process of alternately measuring and changing the gain of each element of the array successively until the gains of all the elements are equal.

2. A device as in claim 1 wherein said controlled atmosphere is a high-vacuum.

3. A method as in claim 1 wherein:

(a) the conductive secondary electron emissive coating on the inner surface of each element is only partially oxidized prior to measuring and changing the gain characteristics thereof,

(b) said controlled atmosphere is a low-pressure atmosphere of oxygen,

(0) the gain of individual elements being changed by the heating and further oxidization of the partially oxidized emissive coating when hit by the high energy electron beam resulting in an increase in gain.

References Cited UNITED STATES PATENTS 4/1964 Goodrich et al. 250--207 8/1967 Eberhardt 250207 US. 01. X.R. 250-207; 313 

